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Shindell and colleagues used a comprehensive computer model and climate simulator — one of the first capable of accounting for the role of short-lived particles expelled in vehicle fumes called aerosols — that shows vehicle fumes exact an enormous toll in all countries and especially in the developing world.

The scientists used modeling techniques developed at GISS to compare a baseline scenario that assumes existing emission standards remain unchanged in coming decades with a second scenario that has most countries adopting stringent standards similar to those in place in Europe and North America. Vehicles in those two regions produce less particulate matter and less polluting gases, such as nitrous oxides and carbon monoxide, due to the use of particle filters and cleaner-burning fuels.

The aggressive scenario assumes, for example, that China, India, and Brazil adopt "Euro 6" standards by 2015, a regime that would reduce emissions of particulate matter by about 85 percent, nitrogen oxides by about 65 percent, and carbon monoxide by about 70 percent for passenger vehicles. The aggressive scenario assumes major emissions reductions in Latin America, Africa, and the Middle East, the regions with the laxest emissions standards. Emissions rules in North America are slightly more stringent than European standards already, so in North America the baseline and aggressive scenarios were identical.